1. Field of the Invention
The present invention relates generally to electrical signal mixers and more particularly to a novel broadband double balanced mixer which uses active elements for frequency conversion of communication signals at microwave frequencies.
2. Brief Description of the Prior Art
Microwave mixers are normally employed in an electrical circuit to convert a high frequency signal to a lower frequency signal in order to simplify signal processing. Double balanced mixers are commonly used in communications equipment and a variety of electronic instrumentation wherever it is necessary to convert an incident signal at a first frequency into an output signal at a different frequency. This is usually done by additive or subtractive mixing wherein an output signal contains frequency components corresponding to multiples of the sum and difference of the frequencies of at least two alternating input signals.
In the prior art devices, producing the necessary frequency balance for the two alternating current input signals generally required the use of two center-tapped transformers or the use of passive baluns. Both transformers and baluns, however, require an expansive amount of circuit space and are relatively expensive. Additionally, transformers are inherently limited in frequency range, a significant drawback in most communications applications.